1. Field of the Invention
The present invention relates to a lithographic exposure technique for use in manufacturing semiconductor devices and the like, and more particularly, to a technique for correcting changes in the transfer magnification of a mask pattern.
2. Description of the Related Art
Recently, the fineness of circuit patterns has increased so that devices such as large-scale integrated circuits (LSIs) may have a higher level of integration and a higher operating speed. As an exposure technique expected to be employed in the future in manufacturing these LSIs, much attention is currently being focused on an X-ray exposure method that forms fine circuit patterns by using high-intensity X-rays from an SR (synchrotron radiation) source or the like. An X-ray proximity exposure method is also proposed. This method uses soft X-rays having wavelengths ranging from 0.5 nm to 2 nm. In an optical system utilized in this X-ray proximity exposure method, for example, X-rays emitted from a source are enlarged to a predetermined field size by an X-ray mirror and are radiated through an X-ray mask onto a wafer substrate that opposes the X-ray mask, thereby transferring a pattern onto the wafer substrate.
An apparatus that uses the X-ray proximity exposure method described above is different in structure from a conventional optical exposure apparatus that uses ultraviolet rays and the like, and, it is difficult to adjust the magnification for exposure transfer onto the wafer substrate through the use of the X-ray optical system. This is an inherent problem of the X-ray optical system that arises because a magnification correction made by an optical system composed of lenses is difficult to apply to the X-ray optical system.
Accordingly, there is a proposal of using a magnification correction method for the X-ray exposure apparatus that positively deforms a mask substrate by applying an in-plane stress or an out-of-plane stress thereto in order to thereby control the magnification of a pattern on a mask membrane of the mask substrate. U.S. Pat. No. 4,592,081 discloses a method that applies an in-plane stress to the mask substrate. In this method, a clamp mechanism of a mask chuck is provided with a mechanical means using an electrostrictive device, and a mask support frame is deformed by the mechanical means, whereby a mask substrate mounted on the mask support frame is expanded and contracted.
Since the pattern on the mask membrane is expanded and contracted by externally applying the force to the mask in the above-mentioned conventional magnification correction method, for there to be magnification correction with high reproducibility, it is important that the point of action of the external force applied to the mask always be fixed.
Strictly speaking, the surface of the mask membrane and the surface on which a mask is supported (i.e., the mask chucking surface) are, however, typically not parallel due to manufacturing tolerances. Therefore, an adjustment of the attitude of the mask is required in order to maintain a uniform exposure gap between the mask membrane and the wafer substrate. Furthermore, the surface of the wafer substrate and the surface of the mask membrane must be maintained parallel to each other during exposure. Since, however, the surface of the wafer substrate generally has a shape in the form of wedges or undulations, that is, it is not uniform in thickness, it is necessary to set the exposure gap shot-by-shot in step-and-repeat exposure. The exposure gap is corrected by changing the attitude of the mask.
At this time, if the attitude of the mask varies independently of the magnification correction mechanism, the point of action of the external force to be applied by the magnification correction mechanism is displaced. This creates a concern that the amount of change in the magnification will vary even when the force that is applied before the attitude adjustment is the same as that applied after the attitude adjustment.
The present invention has been made in view of the aforesaid unsolved problem of the prior art, and has as an object the provision of a mask holding device capable of precisely correcting the magnification without varying the amount of change in magnification even when the attitude of a mask varies, an exposure apparatus equipped with the mask holding device, and a device manufacturing method capable of efficiently manufacturing a semiconductor device.
In order to achieve the above object, according to one aspect, the present invention provides a mask holding device including a frame for supporting a mask, a correction mechanism for correcting a pattern on a mask membrane of the mask by applying force to the mask frame, and means for changing at least one of the attitude and position of the correction mechanism, in accordance with the attitude of the mask.
According to another aspect, the present invention provides an exposure apparatus for exposing a mask having a pattern on a mask membrane, and a substrate, placed a small distance apart, the exposure apparatus including a frame for supporting the mask, a mask holding device having a correction mechanism for correcting the pattern by applying force to the mask frame, and means for changing at least one of the attitude and position of the correction mechanism, in accordance with the attitude of the mask.
According to a further aspect, the present invention provides a device manufacturing method including placing a mask having a pattern on a mask membrane, and a substrate, a small distance apart, supporting the mask on a frame, providing an exposure apparatus that includes a mask holding device having a correction mechanism for correcting the pattern by applying force to the mask frame, changing at least one of the attitude and position of the correction mechanism, in accordance with the attitude of the mask, and performing exposure by exposing the substrate to the pattern on the mask, to manufacture a device.
According to the present invention, the point of action and direction of the load to be imposed on the mask always can be constant regardless of the attitude of the mask. As a result, the amount of change in magnification to be corrected does not vary even when the attitude of the mask varies, which achieves magnification correction with an increased precision.